A non-invasive method to estimate the size of myocardial infarcts and the effect of therapeutic measures on reduction of the size, consists of recording 35 electrocardiographic leads from the left anterior chest wall. ST segment elevations and QRS changes are used as indicators of myocardial injury. It is well-known that much of the information derived from the 35 ECG leads is redundant. Data reduction procedures will therefore, be applied to the original lead set of 35 in order to determine a smaller number of leads which contain the same information. Principal component analysis and a data reduction algorithm developed by Lux and co-workers will be used. It is planned to obtain 150 sets of 35 precordial leads from patients with acute anterior and anterolateral infarcts in the CCU of George Washington University Hospital in Washington, D.C. and the Peter Bent Brigham Hospital in Boston, Massachusetts. One hundred records will be used as training set and 50 as test set. The reduction in number of leads should lead to a more practical and useful procedure in the management of patients with acute infarcts.